In the wireless communications field, because of factors such as mutual movement between communications devices, noise, or a radio channel, a signal received by a communications device at a receive end is generally different from a sent signal. To enhance receiving performance, the communications device at the receive end generally needs to equalize the received signal. Generally, the communications device at the receive end needs to perform channel estimation. Considering implementation complexity, an existing mobile communications system generally does not use a blind estimation method but transmits one or more signals pre-known by both a transmit end and a receive end, so as to implement the channel estimation. For example, in an LTE system, user equipment (English: User Equipment, UE for short) sends a reference signal, to a base station, that is pre-known by both the user equipment and the base station, so that the base station estimates a radio channel that is from the user equipment to the base station, so as to facilitate subsequent processing.
A reference signal used for the channel estimation is generally pre-known by both the transmit end and the receive end. Therefore, for the transmit end of wireless communications, the reference signal does not carry any information. For a receive end, channel information carried by the reference signal is represented by a difference between a received reference signal and a locally stored reference signal copy.
A technical solution called “comb” frequency division multiplexing (Comb Frequency Division Multiplexing) is used to enable a communications device at a transmit end to transmit, in one symbol, both a reference signal used for channel estimation and a signal that carries to-be-transmitted information. A specific solution is: The communications device at a transmit end divides a frequency resource that is corresponding to the communications device and that is in a symbol into two subcarrier groups; and transmits the reference signal in one subcarrier group, and maps the to-be-transmitted information to another subcarrier group. FIG. 1 shows resource mapping statuses of the reference signal and the signal carrying the to-be-transmitted information that are transmitted in the symbol by a communications device at a transmit end. The frequency resource that is occupied by the sending device and that is in the symbol is divided into 12 subcarriers whose serial numbers are sequentially 1 to 12. Subcarriers with odd serial numbers in the 12 subcarriers are used to map the reference signal, and the reference signal is pre-known by both a transmit end and a receive end; and subcarriers with even serial numbers in the 12 subcarriers are used to map the signal corresponding to the to-be-transmitted information.
A technical problem of an uncontrollable signal peak-to-average ratio exists in the foregoing technical solution. Specifically, a reference signal and a signal carrying information that are mapped by the sending device in one symbol are two random signals. Therefore, from a perspective of a time domain, after the two random signals are added together, single carrier characteristics of the signals are actually damaged. Consequently, a peak-to-average ratio is relatively high. This imposes an excessively high requirement on performance of a radio frequency module of the communications device at a transmit end.